1. Field of the Invention
The present invention relates to a novel polyurethane, a process for producing the same, and a process for producing a polyurethane foam. More particularly, the present invention is concerned with a process for producing a polyurethane which gives a polyurethane having excellent moldability in mold filling, substantially without the necessity of using a catalyst component commonly used for producing a polyurethane, a polyurethane produced by the process, a process for producing a rigid polyurethane foam excellent in mold filling, thermal insulation property and low-temperature dimensional stability, a process comprising a spray step for producing a rigid polyurethane foam having excellent mechanical properties and adhesive property, whereby the reaction of a polyol with an isocyanate can sufficiently proceed at low temperature, and a process for producing a foamed-in-mold flexible polyurethane foam for use in furniture and automobile cushions. More particularly, the present invention relates to a process for producing a flexible polyurethane foam by using a urethane feedstock containing a particular tertiary aminoalcohol and having an excellent high temperature moldability at the time of pouring of a urethane feedstock in mold foaming.
2. Description of the Related Art
Polyurethanes are used in various industrial fields, such as in the formation of elastomers, rigid foam, semirigid foam, flexible foam and microcellular foam, by virtue of their easiness of control of molding density, hardness of products and various properties, and their excellent moldability. In producing these polyurethanes, it is a common practice to use a tertiary amine or an organometallic catalyst as a polyurethane producing catalyst, in addition to a polyisocyanate component, and a polyol component for the purpose of promoting curing or foaming, which enables a polyurethane to be produced on an industrial scale.
Among the polyurethane producing catalysts, tertiary amines are widely used because they are useful for controlling the balance of the reaction. In many cases, however, they have a strong irritating odor, and cause skin irritation, and therefore cause problems in the working environment, and have the drawback that the odor lowers the value of the product.
Therefore, the present inventors have proposed using a tertiary amino alcohol represented by the general formula (0): ##STR1## in which R.sub.a is a C.sub.2 to C.sub.24 straight-chain or branched alkylene group, an alicyclic alkylene group, an aralkylene group or --(CH.sub.2 CH.sub.2 O).sub.p --(CH.sub.2 CH.sub.2).sub.q --(where p is 0 or a positive integer and q is a positive integer), R.sub.b is a C.sub.1 to C.sub.24 straight-chain or branched alkyl group or an aralkyl group and 1 is a positive integer of 2 to 50, as a catalyst and a raw material for polyurethane production (Refer to U.S. patent application Ser. No. 563712).
Further, when a rigid polyurethane foam or the like is molded by mold foaming for a use in a refrigerator or a panel, an improvement in the mold filling relating to the fluidity of the resin within a mold is required, so that a method for lowering the density in a high yield has been desired in the art.
In recent years, the use of chlorofluorocarbons as a foaming agent has been legally regulated for the protection of the ozonosphere, and trichlorofluoromethane (R-11), which has hitherto been used for the production of a rigid polyurethane foam, is among the substances subject to the regulation. This brings about a problem of the necessity of reducing the use of trichlorofluoromethane. Examples of the reduction means proposed in the art include one wherein the amount of water used is increased to reduce the amount of trichlorofluoromethane (the so-called "chlorofluorocarbons-poor formulation") and one wherein use is made of 1,1-dichloro-2,2,2-trifluoroethane (R-123) or 2,2-dichloro-2-fluoroethane (R-141b), having ozone destruction factors (ODP) smaller than that of trichlorofluoromethane.
In the chlorofluorocarbons-poor formulation wherein the amount of water used as a foaming agent is increased, the increase in the amount of water inevitably accelerates the reaction of water with the polyisocyanate component. This causes the amount of formation of a urea bond derived from the evolution of carbon dioxide to be increased, so that the balance between the foaming reaction and the resinification reaction is lost, which causes the mold filling of the polyurethane form to be significantly lowered. The use of 1,1-dichloro-2,2,2-trifluoroethane or 2,2-dichloro-2-fluoroethane instead of trichlorofluoromethane makes it necessary to increase the amount of use of water, because the low temperature dimensional stability, compressive strength and mold filling are lowered thereby. This, however, causes the mold filling to be further lowered.
The rigid polyurethane foam, produced by a process comprising a spray step (a spray type rigid polyurethane foam, hereinafter), is used mainly for the thermal insulation of the internal wall and ceiling of houses, and the thermal insulation of tanks. A special foaming machine is used for the foaming work of the spray type rigid polyurethane foam. An air spray foaming machine is a system wherein compressed air is introduced into a mixing gun, while an airless foaming machine is a system wherein a feedstock is introduced into a mixing gun through the use of a lightweight compresser, and then sprayed. A liquid mixture comprising a polyol component and an isocyanate component is sprayed on a face of an article through the use of the above-described foaming machines, and a thermal insulation layer, comprising a rigid polyurethane foam, is formed on that face through the utilization of the properties of the mixture of rapidly thickening, foaming and forming a high-molecular weight polymer.
The above-described useful spray type rigid polyurethane foam has found an expanded application, and an increase in the amount of use thereof has brought about various problems. One of the problems is that the bonding strength between the foam and the adherend material is so poor, that the foam peels off or falls down with the lapse of time to impair the thermal insulation effect, so that dewing becomes liable to occur.
Further, the regulation of the use of chlorofluorocarbons such as trichlorofluoromethane has brought about a tendency to increase the amount of incorporation of water in the foaming agent which further renders the above-described problems serious. Specifically, when the amount of the chlorofluorocarbon subject to the regulation is reduced by increasing the amount of incorporation of water, the agglomeration caused by a urea bond formed by the reaction of water with the isocyanate violently occurs, and further the boundary between the urethane foam and the adherend or the surface of the foam suffers from less accumulation of the heat of reaction, which brings about drawbacks, such as a lack in the self-bonding strength which is the most important property of the spray type rigid polyurethane foam, and an increase in the fragility. This tendency becomes conspicuous in conducting the spraying at a relatively low temperature of 5.degree. C. or below.
The flexible hot mold foam is produced by blending and sufficiently mixing a polyether polyol, a polyisocyanate, a foaming agent, a silicone foam stabilizer and a catalyst with each other, pouring the mixture into a mold and then heating the mixture to allow a reaction to proceed. In this case, after the temperature of the mold is adjusted to 35.degree. to 45.degree. C., a urethane feed-stock is poured into the mold to conduct foaming, and cured in a furnace at 160.degree. to 200.degree. C., and the cured foam is demolded. The reason why the temperature of the mold is adjusted to 35.degree. to 45.degree. C. resides in that when it is below 35.degree. C., an increase in the foam density and insufficient curing of the foam are liable to occur and further the time taken from the pouring to the demolding is lengthened, which hinders the production of the foam. When the temperature of the mold exceeds 45.degree. C., a crack occurs within the foam, so that no good product can be obtained. Although trichlorofluoromethane is used in the production of a foam having a low density and a low hardness, it is desired to reduce or discontinue the use of trichlorofluoromethane for the reasons mentioned hereinabove.
Therefore, if a good foam can be uniformly produced at a mold temperature of 45.degree. C. or above, the step of cooling the mold after the demolding of the foam in a foam production line can be remarkably omitted, which contributes to the prevention of energy loss. Further, the foam produced at a higher mold temperature has a lowered density due to an enhancement in the foaming efficiency. In attaining the same density as that of the foam at an ordinary mold temperature, the amount of the foaming agent can be reduced, whereby the use of the chlorofluorocarbons subject to the regulation can be reduced or discontinued.